S.D. Codified Laws § 32-9-8.1
All fees for a commercial vehicle apply to the power unit or tractor only. In the case of individual power units pulling interchangeable trailers or semitrailers, the commercial motor vehicle shall be licensed according to the largest gross maximum weight the power unit will haul. Each trailer or semitrailer shall have an identification plate displayed in a conspicuous manner as may be prescribed by the Department of Revenue.
The fee for the identification plate is ten dollars. The identification plate when issued is valid for the useful life of the trailer or semitrailer. However, if the title to the trailer or semitrailer is transferred the new owner shall within thirty days of the date of transfer make application to the Department of Revenue for a new identification plate. All revenue raised by the fees shall be placed in the license plate special revenue fund. A trailer licensed with an identification plate pursuant to this section may be pulled by a commercially licensed power unit or by a noncommercial power unit licensed for the gross weight of the motor vehicle. A violation of this section is a Class 2 misdemeanor.
SDCL 32-9-8.1